title: Leaching mechanisms of Cr(VI) from chromite ore processing residue.
abstract: Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from chromite ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values <5, the concentration of total Cr exceeded that of Cr(VI) with the difference between the two attributed to Cr(III). Geochemical modeling results indicated that the solubility of Cr(VI) is controlled by Cr(VI)-hydrocalumite and Cr(VI)-ettringite at pH >10.5 and by adsorption at pH <8. However, experimental results suggested that Cr(VI) solubility is controlled partially by Cr(VI)-hydrocalumite at pH >10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.
authors.affiliation: Center for Environmental Systems, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, NJ 07030, USA. mwazne@stevens.edu
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Wazne
authors.forename: Santhi Chandra
authors.initials: SC
authors.lastname: Jagupilla
authors.forename: Deok Hyun
authors.initials: DH
authors.lastname: Moon
authors.forename: Christos
authors.initials: C
authors.lastname: Christodoulatos
authors.forename: Agamemnon
authors.initials: A
authors.lastname: Koutsospyros
mesh_terms: D002857:Chromium / Q000737:chemistry*; D003198:Computer Simulation; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D008906:Mining; D008956:Models, Chemical; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D014874:Water Pollutants, Chemical; D002857:Chromium